license: exclude ignored files from the license check (#9578)

Previously, if you built the docs, you'd get license errors for
generated .rst files. This removes them from the list of licensed
files.

lib/spack/spack/cmd/license.py

@@ -40,7 +40,7 @@
     r'^lib/spack/env/cc$',
 
     # rst files in documentation
-    r'^lib/spack/docs/.*\.rst$',
+    r'^lib/spack/docs/(?!command_index|spack|llnl).*\.rst$',
     r'^lib/spack/docs/.*\.py$',
 
     # 2 files in external